Summary: In this research, we aim to generate expressions of a robot based on internal state of living state using the robot's breath. Our research focused on the effectiveness of the breath as one of the physiological phenomena, and we implemented the breathing mechanism for a stuffed-toy robot with simultaneous controls of the abdominal motion, breathing motion, and air flows, in order to evaluate the expressiveness of the mechanism. The focus of this paper is 1) the verification of the user's perception of the living or dead state of the robot through the gradual change of the breathing speed, and 2) the modality of the expressions via factor analysis based on SD method using 23 adjective pairs related to emotion, physiology, perception and personality. The results showed that the breathing expression generates the user's perception of the living state of the robot, and the robot's breathing speed expresses the internal state of the robot related to the livery factor.